When excess of carbon dioxide is passed through lime water, the milkiness disappears because (A) water soluble calcium carbonate converts to water soluble calcium bicarbonate. (B) insoluble calcium carbonate converts to water soluble calcium bicarbonate. (C) water soluble calcium carbonate converts to insoluble calcium bicarbonate. (D) insoluble calcium carbonate converts to insoluble calcium bicarbonate.

ScienceCBSE Class 10 · Sample paper, session 2025-26 · 1 mark · MCQ

CBSE Class 10 Science sample paper 2025-26: question 22

From the official CBSE sample question paper for 2025-26, section B, question 22, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q22 · 1 mark · MCQChemical Reactions and Equations

When excess of carbon dioxide is passed through lime water, the milkiness disappears because

(A)water soluble calcium carbonate converts to water soluble calcium bicarbonate.
(B)insoluble calcium carbonate converts to water soluble calcium bicarbonate.
(C)water soluble calcium carbonate converts to insoluble calcium bicarbonate.
(D)insoluble calcium carbonate converts to insoluble calcium bicarbonate.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

Open one hint at a time and try again before the next.

Hint 1

What makes lime water milky in the first place: a soluble or an insoluble substance?

Hint 2

Excess CO₂ reacts further with that substance. Is the new product soluble?

Step-by-step solution

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Lime water turns milky with $C O_{2}$ because insoluble calcium carbonate forms: $C a (O H)_{2} + C O_{2} \to C a C O_{3} ↓ + H_{2} O$ .
With excess $C O_{2}$ , this carbonate changes into soluble calcium hydrogencarbonate: $C a C O_{3} + H_{2} O + C O_{2} \to C a (H C O_{3})_{2}$ (soluble). The milkiness therefore disappears.
The correct description is insoluble carbonate → soluble bicarbonate, option (B).
1 mark

Answer: Option (B)

Where the marks are

Identifies conversion of insoluble CaCO₃ to soluble Ca(HCO₃)₂, option (B) (1 mark)

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Chapter: Chemical Reactions and Equations (notes, formulas, where marks are lost and every past question)

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CBSE Class 10 Science sample paper 2025-26: question 22

Hints

Step-by-step solution

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